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View Full Version : Rim thickness and wear



ronwalf
09-05-2013, 03:02 PM
I noticed my rims were somewhat dished after 6500 miles. I alternated between worrying about them blowing and convincing myself I had another 3500 miles on them, but somehow ended up buying an Iwanson caliper (http://www.amazon.com/gp/product/B0087HKWCO/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1) to measure how thick the rims are.

The minimum rim thicknesses are:

Front CR-18 (http://sun-ringle.com/road/rims/cr18/): 1.05mm, just under the clincher lip
Back VO Diagonale (http://store.velo-orange.com/index.php/components/wheelsets-rims-hubs/rims/vo-diagonale-700c-rims.html): 1.25mm, somewhere around the middle


Researching this isn't helping much:

Jobst Brandt blows his at 0.5mm (http://yarchive.net/bike/rim_wear.html)
These guys seem to blow their rims around 0.6mm (http://www.bikeradar.com/forums/viewtopic.php?p=15342313)
Bicycle Quarterly claims 0.7mm (http://janheine.wordpress.com/2012/05/09/rim-weight/)
Others say it's worn out at 1mm. (http://bike-works.blogspot.com/2009/01/bike-rims-wear-out.html)


I'm hauling the eldest to school this year in his iBert over the front wheel, so the lack of consensus gives me the jitters. Sadly, I'm getting the impression that the only people who know are the engineers who designed the rims.


Contributing factors:

Sloppy weather
Sloppy about cleaning up after said weather (since repented)
Attempting and failing to track stand at every stop sign/light (16 per work day)
Brief use (500-1k miles or so) of VO brake pads ("http://store.velo-orange.com/index.php/components/brakes/pads-shoes/vo-pads-for-road-shoes.html') which act like sand paper (but don't squeal. yay?)

DSalovesh
09-05-2013, 06:13 PM
I've never had a rim failure like this. Other factors have caused rim damage or loss before I've had to worry about wear and tear.

Other variables beyond thickness may come into play. Smooth road surfaces would put less stress on rims, while potholes, cracks, and curb bumps would put more - and we definitely have more of the latter. Spoke tension might have an effect on how much flex rims are subjected to. Brake design may allow higher or lower clamping pressure requiring more or less rim strength before failure, and the use of brakes to modulate speed versus stopping quickly in traffic would also change the forces involved.

This falls into my broad category of things I'd rather not lose sleep over. While it appears the effects of brake track failure aren't especially catastrophic to the wheel itself (similar to tire bead blowout), the effects of potentially losing control in traffic are incalculable. I turn to the other side of the equation: what is to be gained from keeping these rims in service as long as possible? Replacement is somewhere in the future regardless, and you're approaching the point where failure wouldn't be surprising, so I tend to think it's at least time to start shopping around.

Seems like the exact replacement rims would cost about $100 total, plus the meditative work of transferring them over spoke by spoke and truing them up, so there's not much downside.

mstone
09-05-2013, 06:49 PM
<looks smugly at the disk brakes on the commuter>

ronwalf
09-05-2013, 08:57 PM
<looks smugly at the disk brakes on the commuter>

See, I could just go an get this (http://www.treefortbikes.com/product/333222373552/113/Handspun-700c-Front-Wheel.html), but then I'd have to buy a whole new bike to match. Grad student salaries... are what they used to be.

I'll probably just wait a few months and pick up a new CR-18 and re-lace the front wheel. I'm not sure I want to do that for the back given the stresses rear spokes face.

Harry Meatmotor
04-02-2014, 01:25 PM
figured I'd throw in my two pennies since it's a slow news day.

I've only personally seen 3 or 4 failures of a rim due to just rim wear giving way to tire pressure while riding. these were catastrophic failures, one, according to the customer, caused him to need several stitches in his calf after getting skewered. just the thought of that makes me loathe to try and eek out another few hundred miles from a worn rim.

What happens more often than just sheer tire pressure (and even at only like 60PSI, that's 60PSI exerting itself along the entire circumference of the rim!), cracking a rim at the brake track is that some sort of impact weakens the rim. imagine this scenario. Me JRA on my old beat up rain bike, tires at a low pressure, hit a pothole, pinch flat. little do i know, a small crack just formed because the brake track is worn and more proned to bending. I pop a new tube in, smartly inflate to a proper tire pressure, and get an earful of rapid decompression.

luckily i wasn't on the bike, but regardless, the rim is toast.

I've always heard 1mm, and that's what i preach. a 100% safety factor over Jobst Brandt ain't a bad idea, imho.